Cryosurgical system with pressure regulation

ABSTRACT

A surgical cryoablation system comprising a valve having a valve inlet and a valve outlet the valve inlet connectable to a source of cryogenic fluid at a pressure of greater than 4000 psi and the valve outlet connectable to a cryoablation probe, such that the valve outlet is in fluid communication with the cryoprobe such that the source of cryogenic fluid is in fluid communication with the valve inlet.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication No. 62/663,808, filed Apr. 27, 2018, and titled“CRYOSURGICAL SYSTEM WITH PRESSURE REGULATION, the entire content ofwhich is incorporated herein by reference.

BACKGROUND

Cryosurgical systems can be used for cryoablating target tissues (e.g.,a tumor). During cryosurgery, for instance, a surgeon may deploy one ormore surgical tools, such as cryoprobes to cryoablate a target area of apatient anatomy by placing the cryoprobe at or near the target area ofthe patient anatomy. In one example, a cryoprobe utilizes theJoule-Thomson (J-T) effect of a heat transfer medium or fluid suppliedunder pressure to produce cooling. Expansion of the pressurizedcryofluid as it passes through a J-T orifice results in temperatures ator lower than those necessary for cryoablating a tissue in the vicinityof the tip of the cryoprobe. Heat transfer between the expandedcryofluid and the outer walls of the cryoprobe can be used to form aniceball, and consequently cryoablate the tissue.

In cryosurgical systems, the cryofluid may be supplied to the cryoprobesat a pressure which causes freezing of tissue during a freezingprocedure and supplied at a lower pressure for thawing tissue during athawing procedure. There may be one or more cycles of freezing andthawing during a cryoablation procedure.

Cryosurgical systems include one or more cryoprobes connected to one ormore cryofluid sources. Such systems are described in thecommonly-assigned patent, U.S. Pat. No. 8,066,697 and in publishedapplication, U.S. Pub. No. 2010/0256620 A1, the contents of which arehereby incorporated by reference in its entirety. Such systems provideseparate supply and pressure control systems for high and low pressurecryofluids and so are relatively heavy, bulky and more expensive toproduce.

SUMMARY

Systems and methods disclosed herein provide a heat transfer medium,such as a cryofluid (liquid/gas) to transfer heat between a surgicaltool and surrounding tissue of a patient during a surgical procedure.The systems and methods disclosed herein permit pressure regulation ofthe heat transfer medium during the surgical procedure.

In an embodiment, the pressure regulation system includes a pressurecontrol valve that can be actuated to an open state to permit passage ofa heat transfer medium therethrough toward a surgical tool. The pressurecontrol valve can be actuated to a closed state so as to restrict thepassage of the heat transfer medium therethrough. It is preferred thatthe pressure regulation system includes a control system that controlsactuation of the pressure control valve according to one or more controlalgorithms.

A further embodiment provides a first control algorithm for use inactuation of the pressure control valve to open and closed states. Thecontrol algorithm can, for example, be executed by the control system.The control system can, according to the first control algorithm,determine whether the pressure of the heat transfer medium is less thana minimum set-point pressure, and if so, output a first signal to avalve actuator to open the pressure control valve. The control systemcan, according to the first algorithm, also determine, whether thepressure of the heat transfer medium is above a maximum set-pointpressure, and if so output a second signal to a valve actuator to closethe pressure control valve.

In a further optional embodiment, after the pressure control valve isclosed, the pressure may not decrease, and may continue increasinginitially before decreasing. In such optional embodiments, the controlalgorithm can include a second control algorithm that can performsubstantially the same steps as the first control algorithm, butadditionally, determine, whether the pressure of the heat transfermedium reaches and/or exceeds a first pressure after the pressurecontrol valve is closed. If so, the second control algorithm canadvantageously adjust the minimum pressure set-point by an offset.

In further optional embodiments, the offset can be equal to a differencebetween the first pressure and the maximum pressure set-point and theminimum pressure set-point can be lowered by an amount generally equalto the calculated offset.

According to the second control algorithm, the subsequent opening of thevalve can be adjusted by determining, after the pressure control valveis closed and prior to the subsequent opening of the pressure controlvalve, whether the pressure of the heat transfer medium is at or lessthan a second pressure, corresponding to the adjusted value of theminimum pressure set-point. If so, the second pressure, send a thirdsignal to open the pressure control valve.

In further optional embodiments, the first pressure is, optionally,greater than maximum pressure set-point. Such an embodiment, in effect,may permit the opening and closing of the pressure control valve toinclude control system effects (for example, built-in delays, pressureblockages, etc.) and permit controlling the pressure of the heattransfer medium to generally equal a desired nominal pressure.

In a further optional embodiment, the control system can automaticallyindicate a fault condition if the pressure control valve is not closedin response to the second signal.

In one such optional embodiment, the elapsed time after the pressurecontrol valve is opened can be compared to a predetermined time. If thepressure control valve remains open beyond the predetermined time, thepressure control valve can be closed and/or a fault condition can begenerated. Preferably, the predetermined time can be greater than thetime over which the pressure control valve remains open when controlledaccording to the first and/or second algorithms.

In a further preferred embodiment, in the absence of a fault condition,the pressure control valve is in the open state for a first duration. Insuch embodiments, the predetermined time is greater than the firstduration.

A surgical system, such as a cryosurgical system, may comprise such anembodied pressure regulation system which in use is connected to conveya heat transfer medium from a source to a surgical tool.

In a further embodiment, there is provided a cryosurgical systemcomprising a pressure regulation system for performing one or morecryosurgical procedures (cryoablation, cryogenic freezing followed bythawing, cautery, etc.) The cryosurgical system can have at least onecryoprobe with a distal operating tip located in a distal section. Thecryoprobe can receive a heat transfer medium for performing acryosurgical procedure. The pressure control valve can be fluidlycoupled to the cryoprobe and can regulate the pressure of the heattransfer medium supplied to the cryoprobe so as to permit uniform heattransfer between at least the distal section of the cryoprobe.

Optionally, the pressure regulation of heat transfer medium may only beperformed during thawing following a freezing operation. In suchembodiments, the control system can determine whether the cryosurgicalsystem is performing a freeze operation, a thaw operation or a cauteryoperation, for example, based on an operator input.

In further embodiments, the heat transfer medium can be in a cryogenicstate at the distal tip to freeze and/or cryogenically ablate tissuesurrounding the cryoprobe during a freeze operation. The heat transfermedium can be in a non-cryogenic state at the distal tip during a thawoperation (or a cautery operation).

In an optional embodiment, the heat transfer medium can be argon. Theheat transfer medium can be at a pressure of about 3500 psi (about 250bar) upstream of the one or more pressure control valves, and expandfrom the pressure of about 3500 psi when reaching the distal tip of thecryoprobe to produce iceballs and/or to cryoablate tissue.

In a further optional embodiment, the heat transfer medium can be argonand can be regulated to a pressure of between about 200 psi (about 14bar) and about 1000 psi (about 70 bar) starting from a pressure of about1000 psi to about 4000 psi. In such embodiments, the pressure of argonupstream of the pressure control valve can be 3500 psi, and whenpressure regulation is performed using one or more of the controlalgorithms disclosed herein, can be at a pressure of between about 200psi and about 1000 psi.

In further optional or additional embodiments, multiple cryoprobes caneach be connected to a pressure control valve (for example by a manifolddesign). In such embodiments, each cryoprobe can be independentlyoperable relative to other cryoprobes, such that the control system candetermine the maximum pressure set-point and the minimum pressureset-point corresponding to each cryoprobe, and open and close thepressure control valve connected to each cryoprobe based on thecorresponding maximum pressure set-point and the minimum pressureset-point.

In further optional embodiments, each pressure control valve iselectrically actuable, for example, a solenoid valve. In such cases, thecontrol system is in electrical communication with each pressure controlvalve.

In further optional embodiments, each cryoprobe comprises an electricalheater for providing heat during the thaw operation. In such cases, theheat transfer medium can distribute heat generated by the electricalheater during the thaw operation.

In further optional aspects, a quantity of heat transfer medium flowingthrough the pressure control valve in the closed state can be less thana quantity of heat transfer medium flowing through the pressure controlvalve in the open state and thus, opening and closing the pressurecontrol valve according to control algorithms may, in effect, vary thepressure of the heat transfer medium flowing through the pressurecontrol valve.

The pressure regulation system can, in further optional aspects, includea pressure transducer to measure and/or monitor a pressure of the heattransfer medium. In an optional embodiment, the pressure transducer canbe positioned at the outlet or downstream of the outlet of the pressurecontrol valve.

In an embodiment, a surgical system comprises a pressure regulationsystem for regulating the pressure of a heat transfer medium conveyedfrom a source of heat transfer medium to a surgical tool at a pressurefor causing freezing in a freezing procedure and at a lower pressure forthawing in a thawing procedure, the pressure regulation systemcomprising: a valve arrangement comprising a pressure control valve andan actuator for actuating the valve to an open and a closed state,wherein in an open state the valve allows heat transfer medium flow to asurgical tool and in a closed state the valve resists heat transfermedium flow to a surgical tool; and a controller operably connected tothe valve arrangement for causing selective actuation of the valve tothe open and the closed states, wherein in a thawing procedure thecontroller is responsive to a determined pressure of the heat transfermedium downstream of the valve arrangement to cause actuation of thevalve to an open state when the determined pressure is less than a lowerset-point pressure value and to cause actuation of the valve to a closedstate when the determined pressure is higher than an upper set-pointpressure value thereby generating a thawing pressure which cyclesbetween the set-point pressure values for conveying a pressure over timewhich is less than the pressure for causing freezing.

This pressure range may be adjusted by an adjustment value if it isdetermined for example by a pressure sensor that the pressure exceedsthe range and then the adjustment value may be reduced over multiplethawing pressure cycles. During thawing when fluid pressure is regulatedso as not to cause freezing a heater may heat the fluid for transferringheat energy for thawing frozen tissue.

The details of one or more examples are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic illustrating a surgical system according to anon-limiting exemplary embodiment;

FIG. 2 is a schematic illustrating a cryosurgery system according to anon-limiting exemplary embodiment;

FIG. 3 is a sectional front view of a cryoprobe according to anon-limiting exemplary embodiment;

FIG. 4 is a schematic illustrating a pressure regulation systemaccording to a non-limiting exemplary embodiment;

FIG. 5 is a schematic illustrating downstream connections of thepressure regulation system of FIG. 4;

FIG. 6 is a schematic illustrating various components of the controlsystem according to a non-limiting exemplary embodiment;

FIG. 7 is a flowchart illustrating a control algorithm for regulatingpressure according to a non-limiting exemplary embodiment;

FIG. 8 is a flowchart illustrating another control algorithm forregulating pressure according to a non-limiting exemplary embodiment;

FIG. 9 is an illustration of pressure of the heat transfer medium asmeasured by the pressure transducer when the control algorithms of FIGS.7 and 8 are implemented;

FIG. 10 is a flowchart illustrating another control algorithm forregulating pressure according to a non-limiting exemplary embodiment;and

FIG. 11 is a flowchart illustrating another control algorithm forregulating pressure according to a non-limiting exemplary embodiment.

DETAILED DESCRIPTION

Referring to FIG. 1 there is shown an example of a surgical system 50comprising a pressure regulation system 52 for regulating the pressureof a heat transfer medium or fluid supplied from a fluid source 54 to asurgical tool 56. In a cryoablation surgical system, the surgical toolis a cryoablation probe for receiving fluid at a pressure for causingfreezing in a freezing procedure and at a lower pressure for thawing ina thawing procedure.

The source of fluid may be a pressurized vessel for containing fluidunder a required pressure or a supply line in a hospital for supplyingfluid at a required pressure from a remote source. The pressureregulator is arranged for connection by fluid lines 58, 60 to the fluidsource and the surgical tool for regulating the pressure at which fluidis conveyed to the surgical tool from the source. The pressure regulatorcomprises a valve arrangement including a valve 62 and a valve actuator64 for actuating the valve to an open state which allows fluid flow tothe surgical tool and a closed state which restricts fluid flow. Apressure transducer, or sensor, 66 is arranged to determine or measurethe pressure of fluid flowing to the surgical tool downstream of thevalve and is operably connected to the controller for outputting asignal corresponding with the determined pressure.

A controller 68 of the pressure regulation system is connected by acontrol line 70 to the pressure regulator. In a cryogenic or freezingprocedure the controller causes actuation of the valve to the open stateallowing fluid flow at a pressure which is suitable for generating acryogenic temperature in the surgical tool (a cryogenic generatingpressure). This pressure may be generally the same pressure at which thefluid is stored subject to pressure losses in the system. In a thawingprocedure, the controller controls the pressure regulator so that fluidflow to the surgical tool is at a reduced pressure lower than thecryogenic generating pressure. The lower pressure reduces thetemperature applied by the surgical probe.

The controller is connected to the pressure transducer by control line72 and is arranged to receive an output from the pressure transducer 66corresponding to the pressure determined by the transducer. Thecontroller causes selective actuation of the valve 62 responsive to thedetermined pressure.

In order to reduce pressure in a thawing procedure, the controller 68causes actuation of the valve 62 to open and closed states at respectivelower and upper set-point pressure values for generating a thawingpressure which cycles between the set-point pressure values forconveying a pressure over time which is less than the pressure forcausing freezing (the cryogenic generating pressure). The targetpressure over time is the average effective pressure and is between thelower and upper set-point pressure values. The set-point pressure valuesare predetermined so that flow pressure is lower than the cryogenicgenerating pressure and are dependent on the selected heat transfermedium and other characteristics of the system. At least the lowerset-point value is less than the cryogenic generating pressure andpreferably both of the lower and upper set-point pressure values areless than the cryogenic generating pressure.

The set-point pressure values may be adjusted by the controller duringoperation in the event that the pressure exceeds the set-point pressurevalues (or range of acceptable pressure values), particularly duringthawing if flow pressure is higher than required. If in a thawingpressure cycle pressure exceeds the upper set-point pressure valueadjustment is made to compensate. There are a number of reasons for thecause of this over-pressure as explained in more detail below.

In one example, the controller is arranged to adjust the lower set-pointpressure value by an adjustment value if the pressure exceeds the upperset-point pressure value during a thawing pressure cycle and to causeactuation of the valve to an open state at the adjusted lower set-pointpressure value. This adjustment allows the pressure to decrease during athawing pressure cycle to a pressure which is less than the lowerset-point pressure value to compensate for a pressure which exceeds theupper set-point pressure value. The adjustment between the lowerset-point pressure value and the adjusted set-point pressure value maybe equal to the difference between the over-pressure and the upperset-point pressure value.

In another example, the controller is arranged to adjust the upperset-point pressure value by an adjustment value for a thawing pressurecycle if the pressure exceeds the upper set-point pressure value duringa preceding thawing pressure cycle and to cause actuation of the valveto a closed state at the adjusted upper set-point pressure value. Theadjustment to the upper set-point pressure value may be equal to thedifference between the over-pressure and the upper set-point pressurevalue.

The adjustment values are reduced over multiple thawing pressure cyclesso that over time the adjusted upper and lower set-point pressure valuesalign with the upper and lower set-point pressure values for generatinga target thawing pressure as an effective average between the upper andlower set-point pressure values. Preferably one or both adjustmentvalues are reduced one cycle compared to a previous consecutive cycle.The graph in FIG. 9 shows an example of the pressure cycle duringadjustment as the effective average pressure gradually aligns with thedesired or target nominal pressure.

The surgical tool 56 comprises a supply tube 74. Pressurized fluid inthe supply tube undergoes Joule-Thomson expansion into an expansionregion 76 of the tool causing cooling. When the fluid pressure issufficiently high expansion causes temperatures which are suitable tofreeze tissue. The surgical tool comprises a heater 78 for heating fluidin the supply tube during a thawing procedure. During thawing the fluidis regulated to a lower pressure and does not cause significant cooling,which would otherwise counteract the heat supplied by the heater. Thecontroller 68 is operably connected to the heater by control line 80.The controller outputs a signal to the heater to cause heating whenthawing is required.

The supply tube 74 is spaced from an inner housing wall of the surgicaltool to define a fluid passage 82 for conveying fluid away from theexpansion region to an exhaust 84, either for recirculation to the fluidsource, or exhausting to atmosphere or for containment.

In the following description there are described further examples of asurgical system, such as a cryosurgical system, including more detailedexplanation and numerous modifications which may be included in theabove example or other examples. For instance, any aspect of thedisclosure relating to pressure regulation system 200 described belowapply also to pressure regulation system 52 described above andsimilarly to control systems 68 and 310.

Referring to FIG. 2, a pressure regulation system 200 is shown for asurgical system. The surgical system can be a cryosurgical system.However, it should be understood that the pressure regulation system 200is not limited to the cryosurgical system.

Overall System

FIG. 2 is a schematic of a cryosurgery system 10. Components of thesystem can be compactly packaged inside a system housing 12. Thecryosurgical system comprises one or more fluid sources 14. The fluidsources 14 can supply a heat transfer medium, or fluid, duringcryosurgery. For example, the heat transfer medium can be fluids such asargon, nitrogen, air, krypton, CO2, CF4, xenon, and various other gases.In an example, the fluid source 14 can simply be a pressurized vessel orcanister. In certain advantageous aspects, the cryosurgery system 10 canbe in the form of a portable desktop console. In some such advantageousaspects, the system may have a weight of less than about 50 pounds(e.g., about 44 pounds). Accordingly, such systems can be compactlypositioned in the surgery room thereby reducing space requirements.

The cryosurgery system 10, illustrated in FIG. 2 includes a pressureregulation system 200 that can regulate a pressure of the heat transfermedium supplied from the fluid source 14 to a surgical tool (shown inFIG. 3). As seen from FIG. 2, the pressure regulation system 200includes one or more pressure control valves in fluid communication withthe fluid source 14. The pressure regulation system 200 includes acontrol system 310 for controlling actuation of pressure control valvesS₁, S₂, S₃, S₄, S_(n) according to one or more algorithms, as will bedescribed further below.

Continuing with FIG. 2, the heat transfer medium can be conveyed fromthe fluid source 14 via a fluid source outlet 16 toward a pressureregulation system 200 as will be described further below. Heat transfermedium within the fluid source 14 can be at pressures well-above thedesired pressure. For instance, a pressure of the heat transfer mediumat the fluid source outlet 16 can be about 3500 psi (about 240 bar) orin the range between about 1000 psi (about 69 bar) and about 4000 psi(about 275 bar). The fluid source 14 may be a pressurized vessel orcontainer (e.g., a gas cylinder) containing a heat transfer medium atpressures well above the pressure at the fluid source outlet 16 forinstance between about 5000 psi (about 350 bar) and about 7000 psi(about 480 bar). Accordingly, the pressure of the heat transfer mediumis reduced to a desired level by inclusion of a pressure regulator. Heattransfer medium just downstream (e.g., as the fluid travels toward thecryoprobe) of the pressure regulator can be at a pressure lower than thepressure at the fluid source outlet 16. For example, in some cases, thepressure regulator can reduce the pressure of the heat transfer mediumto less than about 4000 psi (about 275 bar) (e.g., about 3500 psi or 240bar). Optionally, a pressure transducer can be fluidly coupled to thepressure regulator to measure pressure of the heat transfer medium ofthe fluid source 14.

The system shown in FIG. 2 can be of a “closed-loop” type. One suchsystem is described in the commonly-assigned application titled,“Closed-Loop System for Cryosurgery,” and granted as U.S. Pat. No.9,078,733 B2, the entire contents of which is hereby incorporated byreference. In an embodiment of a closed loop system, heat transfermedium is not exhausted to the surroundings after a surgical procedure(e.g., cryosurgery) is completed. Instead, the heat transfer medium isreturned (e.g., by a return pathway) from the flow channels (channel 1,channel 2, channel 3, channel 4, etc. shown in FIG. 5) to the fluidsource 14. Direction control valves (e.g., check valves) may be used toreduce and/or to prevent flow of the heat transfer medium in a directionother than the intended direction (e.g., flow toward the cryoprobe 100or return flow from the cryoprobe 100).

Cryoprobe

As described earlier, the surgical tool may be a cryoprobe 100 such asthe cryoprobe 100 shown in FIG. 3. The cryoprobe 100 comprises anelongate generally cylindrical hollow body or probe shaft 102. The shaftis illustrated in cross-section to show internal components (e.g., atrocar). The probe shaft 102 is formed with an operating tip 104disposed at a section 106 distal from a fluid or control connection forpenetrating through tissues of a patient during deployment. A coupler108 is located at a proximal section 110 opposite to the distal section106. The coupler 108 comprises a pin 111 for connection to a controlsystem 310 and/or source as will be described further below.

The probe shaft 102 can be of substantially small cross section forallowing deployment in tissues of a patient. In an example, the probeshaft 102 has an outer diameter of about 2.1 millimeters. Otherdimensions of the probe shaft 102 are also contemplated. For example,the probe shaft 102 can have an outer diameter of between about 1.5millimeters and about 2.4 millimeters. In addition, the operating tip104 can be made of a pliant material so as to be flexible (e.g.,relative to the proximal portion of the cryoprobe 100) for penetratingsoft tissue.

As seen in FIG. 3, the cryoprobe 100 includes a supply tube 112extending substantially along its length for providing a high-pressureheat transfer medium to the operating tip 104. The supply tube 112 canbe positioned coaxially/concentrically within the probe shaft 102. Thesupply tube 112 can be configured to supply a heat transfer medium(e.g., cryofluid) for forming iceballs on an outer surface of the probeshaft 102 over the distal section 106. In some cases, the supply tube112 can be a capillary tube.

The cryoprobe 100 may include a cryocooler as shown in FIG. 3. Forinstance, the supply tube 112 can terminate in a Joule-Thomson orifice114. The Joule-Thomson orifice 114 can be positioned near the operatingtip 104, so as to permit heat transfer medium exiting the Joule-Thomsonorifice 114 to expand into an expansion chamber for cooling the distalsection 106 and particularly the operating tip. As the heat transfermedium expands in the expansion chamber, it cools rapidly and formsiceballs of different shapes and/or sizes over the outer surface of thedistal section and operating tip 104. The expanded heat transfer mediumin the expansion chamber is colder than the incoming heat transfermedium. The iceballs that are formed as a result of rapid expansion ofthe heat transfer medium can freeze and/or ablate tissue (e.g., atumor).

While an exemplary cryocooler such as a Joule-Thomson orifice 114 isillustrated, it should be understood that other types of cryocoolerssuch as cryogenic dewars, Stirling-type cooler, pulse-tube refrigerator(PTR), Gifford-McMahon (GM) cooler are contemplated within the scope ofthe present disclosure. Further, as briefly noted above, cryofluidswhich may be used for cooling include argon, liquid nitrogen, air,krypton, CF₄, xenon, or N₂O.

The outer surface of the operating tip 104 can be made of a materialhaving a high thermal conductivity, such as a metal or metal alloy foreffectively conducting heat from the patient tissue. Stainless steel isa suitable example of such a material.

Referring again to FIG. 3, a heater 116 can optionally be providedwithin the probe shaft 102 to facilitate thawing and/or cauterizingtissue. The heater 116 may be operated after cooling and iceballformation to thaw frozen tissue. Optionally, the heater 116 may beoperated after completion of a surgical procedure to facilitatedisengagement of the cryoprobe 100 therefrom. As referred to herein,thaw/thawing may interchangeably refer to either of the two procedures,of thawing an iceball in between freeze operations, or operating theheater 116 to facilitate disengagement of the cryoprobe 100.

The heater 116 is arranged to heat the heat transfer fluid as it isconveyed through the supply tube 112 during a thawing part of aprocedure. The heat transfer medium may be at conditions (pressure,temperature, phase, etc.) such that when expanding from the orifice 114,the heat transfer medium may not reach cryogenic temperatures at certaininstances (described below). Instead, the heat transfer medium at theseconditions functions to transfer heat to the distal section 108 andoperating tip for thawing tissue. The heat transfer medium may itself beat a temperature sufficient for thawing or as shown may be heated by theheater 116 to raise the temperature.

An electrical heater 116 can be provided coaxially with the supply tube112 and the probe shaft 102 to facilitate heating the distal section 106of the cryoprobe 100. Alternatively, the electrical heater 116 can bepositioned elsewhere in cryoprobe 100 to heat the distal section 106 ofthe cryoprobe 100. The electrical heater 116 can be a resistive heater116, wherein the electrical heater 116 generates heat proportional tothe current flow therethrough and the electrical resistance ofelectrical heater 116. In such cases, the probe is arranged to connectto a source of electrical power for conveying an electrical current tothe heater 116.

As seen in the FIG. 3 example, the annular area between the supply tube112 and the inner walls of the probe shaft 102 defines a return lumen118 in fluid communication with the expansion chamber for conveyingexpanded heat transfer medium from the expansion chamber. In an exampleof a closed-loop system the heat transfer medium is returned to a fluidsource after each surgical procedure. Alternatively, a system can beoperated in an “open-loop” configuration, and can be exhausted to thesurroundings after use.

Properties of Heat Transfer Medium

In certain examples of the system, the heat transfer medium can be at aninitial state when entering the pressure regulation system 200. Theinitial state can be defined by an initial pressure and an initialtemperature. The initial pressure and the initial temperature can besuch that when the heat transfer medium undergoes expansion, (e.g.,Joule-Thomson expansion through the orifice 114), the pressure and thetemperature of the heat transfer medium may both decrease. When the heattransfer medium undergoes expansion from pressures significantly lessthan the initial pressure, however, a reduction in pressure may not beaccompanied by a reduction in temperature (for instance, to cryogenictemperature). Thus, if it is desirable to provide the heat transfermedium to the distal section 108 in a cryogenic state, the pressure ofthe heat transfer medium entering the pressure regulation system 200 maynot have to be substantially further reduced from the initial pressure.However, if heat transfer medium at a non-cryogenic state is to beprovided to the distal section 108, the pressure of the heat transfermedium can be substantially reduced from the initial pressure by thepressure regulation system 200.

In examples of the system, as described above, if the initial pressureof the heat transfer medium is sufficiently high, the heat transfermedium undergoes expansion, and is cooled. The expansion of the heattransfer medium may cool the heat transfer medium sufficiently such thatthe temperature of the heat transfer medium reduces to cryogenictemperature. For simplicity this sufficiently high initial pressure isreferred to as a cryogenic pressure and varies dependent on the medium(type of the heat transfer medium, such as a gas or liquid, temperatureof the heat transfer medium prior to expansion, and the like) and othercharacteristics of the system. Therefore during a freezing procedure,the pressure regulator is arranged to supply a heat transfer medium at acryogenic pressure taking into account that there are some pressurelosses inherent in the system (e.g. between the pressure regulator andsurgical tool).

During thawing, the pressure of the heat transfer medium is regulated sothat it is less than the cryogenic pressure. Preferably the pressure isregulated so that it less than the cryogenic pressure by a safetymargin. For simplicity this pressure is referred to as a non-cryogenicpressure. Expansion of the heat transfer medium (e.g., the same mediumand under same characteristics as the freezing procedure) from thenon-cryogenic pressure may not reduce the temperature of the heattransfer medium sufficiently to reach cryogenic temperatures.

In an example, the cryogenic pressure may be about 3500 psi (about 240bar), and the heat transfer medium may be argon. The cryogenictemperature generated may be less than about 150 Kelvin and preferablyin the range of 120 to 150 Kelvin. In a freezing procedure, as argonleaves the supply tube 112, it expands from the cryogenic pressurecausing cooling, and reaches a cryogenic state. In a thaw procedure, thesupply pressure of argon is regulated to a non-cryogenic pressure ofless than about 1000 psi (about 70 bar), and preferably less than about700 psi (about 48 bar). When argon undergoes expansion from thispressure, its temperature does not reduce significantly to reachcryogenic temperatures (or generally remains constant). Argon may remainat a temperature of above 150 K, and preferably above 273 K, and maycontinue to increase particularly when heated by the heater 116.

In this regard, the cryoprobe 100 can receive the heat transfer mediumduring the thaw procedure (or cautery). At this point, the heater 116supplies heat to the probe shaft 102 to facilitate removal of the probeshaft 102 from the frozen tissue. Accordingly, in such embodiments, theheat transfer medium can evenly distribute the heat generated by theheater 116 over the surface area of the probe shaft 102, so as to permituniform heat transfer rate between various points on the probe shaft 102and the surrounding tissue. Such embodiments permit ease of removal ofthe probe shaft 102 from the tissue.

Referring back to FIG. 2, heat transfer medium is conveyed from a fluidsource 14 to a pressure regulation system 200 for regulating thepressure of the heat transfer medium. One or more cryoprobes can befluidly connected to and positioned downstream (e.g., as the fluidtravels toward the cryoprobe) of the pressure regulation system 200 suchthat heat transfer medium at a desired pressure can be supplied to thesupply tube 112. The pressure regulation system 200 can adjust thepressure of the heat transfer medium such that the heat transfer mediumis in a cryogenic state during certain portions of a cryosurgicalprocedure and in a non-cryogenic state during certain other portions ofthe cryosurgical procedure.

For instance, the cryoprobe 100 can receive the heat transfer medium ina cryogenic state during the freeze cycle. Accordingly, the pressureregulation system 200 can be configured, as will be described below, toensure that the heat transfer medium leaving the supply tube 112 is atthe cryogenic pressure (e.g., 3500 psi for argon) during the freezecycle. Further the cryoprobe 100 can receive the heat transfer medium ina non-cryogenic state during the thaw operation (and/or a cauteryoperation) to permit heat exchange between the cryoprobe 100 and thetissue surrounding the cryoprobe 100. Accordingly, the pressureregulation system 200 can be configured, as will be described furtherbelow, to ensure that the pressure of heat transfer medium downstream(e.g., as the fluid travels toward the cryoprobe) of the pressureregulation system 200 and/or as the heat transfer medium leaves thesupply tube 112 is less than the non-cryogenic pressure (e.g., less than1000 psi for argon). Advantageously, as described above, providing heattransfer medium in a non-cryogenic state during the thaw operation (or acautery operation) permits evenly distributing heat generated by theheater 116 during the thaw operation (or a cautery operation) such thatheat transfer between the probe shaft 102 and the surrounding tissue (ascharacterized, for example, by temperature of the probe shaft over alength of the probe shaft) during the thaw cycle (and/or cautery) isuniform. Such embodiments may improve ease of removal of the cryoprobe100 once cryoablation is complete.

Pressure Regulation System

Common Inlet to Pressure Control Valves

FIG. 4 is a schematic that illustrates the details of the pressureregulation system 200. In FIG. 4, the solid lines connecting variouscomponents can be fluid lines, or ducts, 204 (e.g., tubes) coupled tothe components of the pressure regulation system 200 by fluid couplings(e.g., mechanical connectors).

As seen in FIG. 4, the pressure regulation system 200 includes aplurality of pressure control valves (S₁, S₂, S₃, S₄, . . . S_(n))controlled by valve controllers. The valve controllers can be integratedinto the pressure control valves (S₁, S₂, S₃, S₄, . . . S_(n)). Thevalve controllers can include electrical/electronic circuitry (e.g.,diodes, field programmable gate arrays, printed circuit board (PCB)processors and the like) that can receive an electrical signal and/orinstructions. The valve controller can optionally include anelectromagnetic actuator that can be energized (e.g., by a voltage orcurrent) or de-energized to move the pressure control valves (S₁, S₂,S₃, S₄, . . . S_(n)) between open and closed states.

In an embodiment, the pressure control valves (S₁, S₂, S₃, S₄, . . .S_(n)) can be configured and arranged in the form of a manifold designand may be referred to as a distribution manifold 210. Referring back toFIG. 2, according to an example, the distribution manifold 210 can behoused within the system housing 12.

In an example, as illustrated in FIG. 4, the distribution manifold 210can optionally have a common manifold inlet 212 upstream of eachpressure control valve S1, S2, S3, S4 and a plurality of valve outlets214 a, 214 b, 214 c, 214 d, . . . 214 n. Each valve outlet (214 a, 214b, 214 c, 214 d, . . . 214 n) is downstream (e.g., as the fluid travelstoward the cryoprobe) of a corresponding pressure control valve (S₁, S₂,S₃, S₄, . . . S_(n)). One or more cryoprobes can be fluidly coupled toeach valve outlet (214 a, 214 b, 214 c, 214 d, . . . 214 n) via acorresponding flow channel (216 a, 216 b, 216 c, 216 d . . . 216 n) aswill be described further below. While four pressure control valves areillustrated, it should be understood that additional or fewer valves arecontemplated within the scope of the present disclosure. In addition,configurations other than a manifold design for arranging andpositioning the pressure control valves are also contemplated within thepresent disclosure.

As shown in FIG. 4, the common manifold inlet 212 can be fluidly coupledto the fluid line 16 that supplies the heat transfer medium. The fluidconnections of the manifold inlet can permit the manifold inlet to be indirect or indirect fluid communication with the fluid source 14, andtherefore receive heat transfer medium directly or indirectly therefrom.

Flow to Cryptoprobes and Return Flow

FIG. 5 illustrates an example of a system for connection to a pluralityof cryosurgical tools so that more than one tool can be used forperforming a procedure. FIG. 5 shows the connections of each of thevalve outlets (214 a, 214 b, 214 c and 214 d). In the illustratedembodiment, each flow channel (216 a, 216 b, 216 c, 216 d, . . . 216 n)is connected to two sub-channels (216 a-1, 216 a-2, 216 b-1, 216 b-2,216 c-1, 216 c-2, 216 d-1, 216 d-2), each being fluidly connectable witha cryoprobe 100. Accordingly, a single pressure control valve (S₁, S₂,S₃, S₄ . . . S_(n) shown in FIG. 3) can be fluidly coupled to twocryoprobes according to the illustrated embodiment. Additional or fewercryoprobes per pressure control valve (S₁, S₂, S₃, S₄, . . . S_(n)) arecontemplated within the scope of the present disclosure. Thesub-channels can be configured in the shape of a fluid port or connectorso as to connect the distribution manifold 210 and components thereof tothe proximal coupler 108 of the cryoprobe 100. For instance, thesub-channels can terminate in a connector that can engage with andconnect to the proximal pin 111 of the proximal coupler 108.Advantageously, in addition to being fluidly connectable to thesub-channel, the proximal coupler 108 can electrically connect (e.g.,via a BNC type electrical connector and/or electrical cables) thecryoprobe 100 with the control system 310 so as to permit the controlsystem 310 to electrically communicate with the cryoprobe 100 before orduring a cryosurgical procedure.

A pressure regulation system can include various optional flowconditioning components as explained with reference for example to FIG.4 to ensure desired properties of the heat transfer medium entering thepressure control valves for various purposes, such as relieving excesspressure in fluid line 204 that conveys heat transfer medium if thepressure in the fluid lines 204 reach and/or exceed a limiting value ofpressure. The limiting value of pressure can be chosen based onoperating conditions as well as safety considerations. The pressureregulation system 200 can also optionally include a pressure transducerfluidly coupled to the fluid line 204 so as to monitor pressure of theheat transfer medium entering the pressure regulation system 200 andconveyed by fluid line 204. Further, optionally, pressure regulationsystem 200 can include a dryer that can be fluidly coupled to andpositioned downstream (e.g., as the fluid travels toward the cryoprobe)of the pressure transducer. Optionally, each flow channel 216 a, 216 b,216 c, 216 d (illustrated fluidly coupled to the valve outlet 214 a, 214b, 214 c, 214 d in FIG. 3) can be fluidly coupled to one or more dryers(e.g., silica gel or other desiccants or dryers). In addition, in somecases, each sub-channel can have a direction control valve to reduce orprevent the chances of heat transfer medium from flowing other than inthe intended direction (e.g., downstream toward the cryoprobe 100, orfrom the cryoprobe 100 back toward the fluid source 14 via a returnpath).

As mentioned previously, the system can be a closed-loop system, wherebythe heat transfer medium, is not exhausted after use, and is insteadreturned to the fluid source 14. FIG. 5 illustrates one such return flowsection 300 according to an embodiment. As seen in FIG. 5, the returnflow section 300 can also be configured as a manifold, and can, in someembodiments, be referred to as a return manifold 304. The returnmanifold 304 can have return flow sub-channels (302 a-1, 302 a-2, 302b-1, 302 b-2, 302 c-1, 302 c-2, 302 d-1,302 d-2). In certainnon-limiting embodiments, the number of return flow sub-channels (302a-1, 302 a-2, 302 b-1, 302 b-2, 302 c-1, 302 c-2, 302 d-1, 302 d-2) canequal the number of flow sub-channels (216 a-1, 216 a-2, 216 b-1, 216b-2, 216 c-1, 216 c-2, 216 d-1, 216 d-2). Each return flow sub-channelcan be in the form of a fluid connection port and can be in fluidcommunication with the return lumen 118 of the cryoprobe 100.

Solenoid Valve Control

A pressure control valve for example as shown in FIGS. 1, 2 and 4 isassociated with a valve control, or actuator, for causing actuation ofthe valve responsive to an output from a system control (e.g controller68 or system control 310). The valve control may comprise a solenoidthat causes or allows movement of a valve member for selectiveengagement with a valve seat. When the valve member is engaged with thevalve seat flow through the valve is restricted (closed state) and whendisengaged flow is permitted (open state). The valve controller caninclude, in one example, an electrical control circuit in communicationwith (e.g., receiving signals and/or instructions from) the controlsystem for energizing a solenoid in response to an output signal fromthe control system. Other types of valves are contemplated within thescope of the present disclosure.

The pressure control valves (S₁, S₂, S₃, S₄, . . . S_(n)) can beactuated to move the pressure control valve (S₁, S₂, S₃, S₄, . . .S_(n)) between a closed state and an open state. In the open state, heattransfer medium received from the common manifold inlet may flow throughthe pressure control valve (S₁, S₂, S₃, S₄, . . . S_(n)) and exit thepressure control valve via the valve outlet (214 a, 214 b, 214 c, 214 d,. . . 214 n), and flow toward the cryoprobe 100(s) fluidly coupled tothe valve outlet (214 a, 214 b, 214 c, 214 d, . . . 214 n). The pressurecontrol valves (S₁, S₂, S₃, S₄, . . . S_(n)) can be normally in theclosed state until they are actively energized (e.g., by an electricalsignal or instructions sent from the control system 310) to move fromthe closed state to the open state.

In certain aspects, in the open state and in the closed staterespectively, the pressure control valves may either be in a fully openand fully closed state or may be partially open and partially closedrespectively. As used herein, the term “close,” “closed,” “closing,” (orvariations thereof) or “closed state” can include both a partiallyclosed state and/or a fully closed state. Further, the term “open,”“opened,” “opening,” (or variations thereof) or “open state” can includeboth a partially open state and/or a fully open state. In certainembodiments, a quantity of heat transfer medium flowing through thepressure control valve in the closed state may be less than a quantity(e.g., flow rate) of heat transfer medium flowing through the pressurecontrol valve when the pressure control valve is open. A quantity (e.g.,flow rate) of heat transfer medium flowing through the pressure controlvalve when the pressure control valve is closed may correspond to aboutzero. The quantity (e.g., flow rate) of heat transfer medium may begreater than zero when the pressure control valve is open.

Pressure Transducer

Referring again to FIGS. 1, 2 and 4, the pressure regulation systems 52,200 can include one or more pressure transducers, or sensors, fordetermining pressure of flow. The control system is arranged to receivean output from the transducer for controlling operation of the pressureregulation system. For simplicity in the following more detaileddescription of the transducers reference is made to the transducersshown in FIGS. 2 and 4, but any aspect of this description appliesequally to sensor 66 in FIG. 1. Each pressure transducer (PT₁, PT₂, PT₃,PT₄, . . . PT_(n)) can be fluidly coupled to a corresponding orassociated pressure control valve (S₁, S₂, S₃, S₄, . . . S_(n)). In someembodiments, the pressure transducers (PT₁, PT₂, PT₃, PT₄, . . . PT_(n))can be provided at the outlet of each pressure control valve. In otherembodiments, the pressure transducers (PT₁, PT₂, PT₃, PT₄, . . . PT_(n))can be provided further downstream of the outlet of each pressurecontrol valve (S₁, S₂, S₃, S₄, . . . S_(n)). In some cases, the pressuremay not vary significantly between the valve outlet (214 a, 214 b, 214c, 214 d, . . . 214 n) and downstream near the body of the cryoprobe.Thus, the location of the pressure transducers (PT₁, PT₂, PT₃, PT₄, . .. PT_(n)) can be customized to be a suitable location downstream of thepressure control valve (S₁, S₂, S₃, S₄, S_(n)).

The pressure transducers (PT₁, PT₂, PT₃, PT₄, . . . PT_(n)) can measurea pressure of the heat transfer medium downstream (e.g., as the fluidtravels toward the cryoprobe) of the corresponding pressure controlvalve (S₁, S₂, S₃, S₄, . . . S_(n)). The pressure transducer (PT₁, PT₂,PT₃, PT₄, . . . PT_(n)) can measure an instantaneous pressure of theheat transfer medium. Alternatively, the pressure transducer (PT₁, PT₂,PT₃, PT₄, . . . PT_(n)) can provide a pressure reading indicative of atime-averaged pressure of the heat transfer medium over a predefinedinterval, such as, by sampling the pressure of the heat transfer mediumover the predefined interval at a predefined sampling frequency. In suchcases, the time interval over which the pressure transducer (PT₁, PT₂,PT₃, PT₄, . . . PT_(n)) collects pressure data, as well as the samplingrate of data collection can be adjusted (as will be described furtherbelow). While the description below relates to the use of pressuretransducers (PT₁, PT₂, PT₃, PT₄, . . . PT_(n)) to provide pressurefeedback to control performance, as is appreciable, the pressuretransducers may provide pressure feedback to control performance duringfreeze cycle as well (e.g., to adjust size and shape of iceballs, etc.)In addition, the pressure transducers (PT₁, PT₂, PT₃, PT₄, . . . PT_(n))may provide an output in the form of pressure of the heat transfermedium, and/or output indicative of the pressure of the heat transfermedium (e.g., an electrical signal, voltage, etc.) One or more signalconditioning circuits (e.g., analog-digital converters, filters 324, andthe like) can be optionally provided to condition the signal provided bythe pressure transducers (PT₁, PT₂, PT₃, PT₄, . . . PT_(n)).

Control System & Circuits

A control system is arranged to control the flow of a heat transfermedium supplied to a cryosurgical tool in order to operate the tool inone of a freezing or a thawing condition. As described herein thecontrol controls actuation of a pressure valve arrangement and at leastin a thawing condition is responsive to an output from an associatedpressure transducer for controlling actuation. Further details of thecontrol system are described below with reference to FIGS. 2 and 4 inparticular but apply more generally to other embodiments.

As described previously, each pressure control valve (S₁, S₂, S₃, S₄, .. . S_(n)) is fluidly connectable to at least one cryoprobe 100 so as toallow the heat transfer medium to selectively flow through the cryoprobe100. Accordingly, certain embodiments of the system also include acontrol system 310 for controlling the valve controllers of the pressurecontrol valves (S₁, S₂, S₃, S₄, . . . S_(n)). The control system 310 canbe a controller in the form of a processor, a gate array (e.g., fieldprogrammable gate array, FPGA), Application Specific Integrated Circuit(ASIC) or a microcontroller in electrical communication (shown by dashedlines in FIG. 1) with various components of the system. The controlsystem 310 can include electrical and/or electronic circuitry that canbe configured for, or programmable to control the operation of the valvecontrollers of the pressure control valves (S₁, S₂, S₃, S₄, . . .S_(n)). The control system 310 can be in operative communication withpressure transducers (PT₁, PT₂, PT₃, PT₄, . . . PT_(n)) and can receivepressure (or signals indicative pressure) measured therefrom.

Referring back to FIG. 2, in certain advantageous aspects, the controlsystem 310 can be housed within the system housing 12 and in electricalcommunication with the pressure regulation system 200. In addition, thecontrol system 310 can also be in electrical communication with thecryoprobes connected to the valve outlets (214 a, 214 b, 214 c, 214 d, .. . 214 n). Further, the control system 310 can include and/or be inelectrical communication with sensors, timers, analog/digitalconverters, wired or wireless communication circuits, etc. In addition,the control system 310 can be operatively connected to an externaldisplay, and input devices (e.g., keyboard, mouse, touchscreen and thelike) for receiving operator input. Alternatively, the control system310 can be an external computer connectable to the system. In suchcases, the external computer can have and/or be programmed with computerreadable instructions so as to perform one or more control and/orsurgical steps, as will be described further below.

FIG. 6 is a schematic that illustrates various components of a pressureregulation system according to an embodiment. In this explanation,reference is made to the pressure regulation system 200 which comprisesone or more pressure transducers (PT₁, PT₂, PT₃, PT₄, . . . PT_(n)) inelectrical communication with one or more signal conditioning components320. In an example, the signal conditioning components 320 can includean analog-digital converter 322 that converts the analog electricalsignals measured by the pressure transducers (PT₁, PT₂, PT₃, PT₄, . . .PT_(n)) into a digital signal. Parameters of measurement such assampling rate and duration over which pressure measurements (e.g., forthe duration of the freeze, thaw or cautery cycle) may be set asappropriate.

With continued reference to FIG. 6, one or more filters 324 can beoptionally provided as a part of the signal conditioning components 320.The filter(s) 324 can advantageously reduce measurement noise and/orprovide anti-aliasing of pressure measurement.

As mentioned above and referring to FIG. 4, the control system 310 canbe in electrical communication with the pressure control valves (S₁, S₂,S₃, S₄, . . . S_(n)). Accordingly, the control system 310 can send anelectrical signal to the pressure control valves (S₁, S₂, S₃, S₄, . . .S_(n)) so as to transition them from the open state to the closed stateor vice-versa. The control system 310 may send an electrical signal tothe pressure control valves (S₁, S₂, S₃, S₄, . . . S_(n)) based onoperating conditions.

In one example, if the control system 310 determines (e.g., based onoperator input) that a freeze operation is to be performed, the controlsystem 310 can send a signal to the pressure control valves (S₁, S₂, S₃,S₄, . . . S_(n)) so as to move them to the open state and/or to maintainthe pressure control valves (S₁, S₂, S₃, S₄, . . . S_(n)) to be in theopen state for a predefined duration (e.g., corresponding to theduration of the freeze operation). This may permit the heat transfermedium from the fluid source 14 to flow through the valve outlet (214 a,214 b, 214 c, 214 d, . . . 214 n) and into the cryoprobe 100.

In another example, if a control system determines (e.g., based onoperator input) that a thaw (or cautery) operation is to be performed,the control system, for example system 310, can send a signal to thepressure control valves (S₁, S₂, S₃, S₄, . . . S_(n)) so as torepeatedly move between an open state and/or a closed state according toa predetermined algorithm. This may permit the heat transfer medium tobe distributed from the fluid source 14 to the cryoprobe at a lowerpressure (e.g., relative to the freeze operation).

With continued reference to FIGS. 4 and 5, in some illustrativeembodiments, each cryoprobe 100 can be independently operable relativeto other cryoprobes. Accordingly, the control system 310 can actuateeach pressure control valve independently of the other pressure controlvalves. The control system 310 can thus actuate each pressure controlvalve selectively so as to selectively control flow of the heat transfermedium into the cryoprobe 100 corresponding to each pressure controlvalve. Additionally the control system 310 can actuate each valve over acertain duration, so as to supply the heat transfer medium in acryogenic or non-cryogenic state, as will be described further below.Such embodiments can beneficially permit different types of cryoprobes(e.g., with different probe shaft outer diameters, and/or differentfreezing/thawing properties) to be connected to the same cryoablationsystem and yet be controlled independently of each other.

As described previously, the control system 310 sends an electricalsignal to each pressure control valve (S₁, S₂, S₃, S₄, . . . S_(n)) totransition the pressure control valve (S₁, S₂, S₃, S₄, . . . S_(n)) intoan open state or closed state. During the thaw cycle, the control system310 can send an electrical signal to the pressure control valve (S₁, S₂,S₃, S₄, . . . S_(n)) to repeatedly switch between the open state and theclosed state according to one of the disclosed control algorithms. Infurther advantageous embodiments, the control system 310 can actuateeach pressure control valve (S₁, S₂, S₃, S₄, . . . S_(n)) selectivelyand independently of each other, resulting in each cryoprobe 100 beingoperable independently of other cryoprobes.

In one example, referring to FIGS. 2 and 5, when a first cryoprobe 100 aperforms the freeze operation, a second cryoprobe 100 b may not performany operation, while a third cryoprobe 100 c performs the thawoperation. The control system 310 can send a first signal to a firstpressure control valve S₁ in fluid communication with the firstcryoprobe 100 a to remain the open state for the duration of the freezeoperation. The control system 310 can send a second signal to a secondpressure control valve S₂ in fluid communication with the secondcryoprobe 100 b to remain closed, and a third signal to a third pressurecontrol valve S₃, repeatedly switch between the open state and theclosed state if the pressure (or data indicative of pressure) measuredby the pressure transducer PT₃ is not within the predetermined pressurerange.

As described previously, in certain embodiments, the heat transfermedium may be at a cryogenic state when leaving the supply tube 112 ofthe cryoprobe 100 for certain cryosurgical procedures (e.g., freeze),and in a non-cryogenic state for certain other cryosurgical procedures(e.g., thaw/cautery). In advantageous aspects of the present disclosure,the pressure control valves (S₁, S₂, S₃, S₄, . . . S_(n)) remain in theopen state for the duration of the freeze procedure. However, thepressure control valves may be repeatedly opened and closed for theduration of the thaw cycle. Appreciably, repetitive opening and closingof the pressure control valves can result in a pressure reductiondownstream (e.g., as the fluid travels toward the cryoprobe) of thevalve outlet (214 a, 214 b, 214 c, 214 d, . . . 214 n), as will bedescribed below.

In some such embodiments, during thawing (or cautery), the pressurecontrol valves (S₁, S₂, S₃, S₄, . . . S_(n)) can be repeatedly openedand closed until a pressure of the heat transfer medium is a desiredpressure set-point (e.g., less than a second pressure). When expandingfrom pressures less than the second pressure, the heat transfer mediumcan advantageously be in a non-cryogenic state such that there may be noiceball formation during a thawing operation.

In one example, if the heat transfer medium is argon, based on thedimensions and/or freeze/thaw properties of the cryoprobe, the pressureset-point can be between about 200 psi (about 15 bar) and about 1000 psi(about 70 bar), for instance, about 500 psi (about 35 bar). Accordingly,the pressure control valves (S₁, S₂, S₃, S₄, . . . S_(n)) can be openedand closed during the thaw/cautery procedure to effectively achieve adesired pressure in the range of pressure set-points (e.g., about200-1000 psi, or 15-70 bar).

As described above, the pressure control valves can be opened and closedto achieve a desired pressure of the heat transfer medium. One or morecontrol algorithms (described further below) can be used to control theopening and closing of each of the pressure control valves (S₁, S₂, S₃,S₄, . . . S_(n)).

Control Algorithms

Algorithm 1—On-Off Control

As described below, a control system (e.g. system 68 or 310) comprises acomputer-readable storage medium comprising a control algorithm which,when executed by the control system, cause the control system to carryout the steps as illustrated for example in FIGS. 7 and 8 and describedherein. FIG. 7 illustrates a control algorithm 600 of regulatingpressure of the heat transfer medium during a thaw cycle (or cautery)according to a non-limiting exemplary embodiment. The steps describedherein (e.g., for algorithms 600, 700, 900 and 1000) may be used foradjusting the pressure in at least one of the flow channels via at leastone of the pressure control valves (e.g., S₁) based on pressuresmeasured by at least one of the pressure transducers (e.g., PT₁).Optionally, the pressure in all the flow channels may be adjusted bysimultaneously and/or sequentially controlling at least each of thepressure control valves (S₁, S₂, S₃, S₄, . . . S_(n)), based onpressures measured by each of the pressure transducers (PT₁, PT₂, PT₃,PT₄, . . . PT_(n)).

At step 602, the pressure transducer (e.g., PT₁) measures pressure andsends the measured pressure (or an electrical signal representativethereof) to the control system 310. The control system 310, at step 604,receives the measured pressure (or an electrical signal representativethereof) and compares it to a minimum or lower pressure set-point. Ifthe measured pressure is less than the minimum pressure set-point value,at step 606, the control system 310 sends a signal to the valvecontroller to open the pressure control valve. The control system 310may continue monitoring the pressure (via pressure received from thepressure transducer) when the valve is open to determine, at step 608,if the pressure reaches and/or exceeds a maximum, or upper pressureset-point. If the control system 310 determines that the measuredpressure reaches and/or exceeds the maximum pressure set-point value, atstep 610, the control system 310 sends a signal (or instructions) to thevalve controller to close the pressure control valve.

In an example implementation of control algorithm 600, the pressureregulation system 200 may receive pressure from the pressure transducerat periodic intervals. For instance, the pressure transducer may samplepressure at predetermined sampling rate (e.g., 2 kHz), and may send themeasured pressure to the control system 310. The sampling rate can bechosen so as to minimize (or eliminate) aliasing, and generatesufficient number of pressure readings.

The control system 310 may compare the measured pressure to the minimumand maximum pressure set-points. If the measured pressure is at or lessthan the pressure set-point, the control system 310 sends a signal orinstructions to the valve controller to open the pressure control valve.In the meantime, the pressure transducer continues to generate apressure measurement at its predetermined sampling rate and send to thecontrol system 310. The control system 310 in turn, continues to monitorthe measured pressure and determine whether the measured pressure iswithin the range pressure set-points (e.g., above minimum pressureset-point and less than maximum pressure set-point).

The minimum pressure set-point and maximum pressure set-point may be setto values based on the type of the cryoprobe and its freeze/thawperformance. The minimum and maximum pressure set-points can both be thesame value or be different values. When the pressure cycles betweenset-points it generates an effective average flow pressure between theset-points and the values of the set-points are predetermined so thatexpansion from the effective average flow pressure would result in thetemperature of the heat transfer medium being non-cryogenic and suitablefor a thawing procedure.

In optional embodiments, the control algorithm 600 may include anoptional step 612, whereby the control system 310 keeps track of timeelapsed after the pressure control valve has been opened and comparesthe elapsed time to a predetermined time at step 614. If the elapsedtime exceeds a predetermined time, at optional step 616, the controlsystem 310 can generate a fault signal to indicate that the flow channel(one or more of 216 a, 216 b, 216 c, 216 d) has faulted if thepredetermined time has elapsed. At optional step 618, the control system310 can send a signal (or instructions) to close the pressure controlvalve.

In an example implementation of control algorithm 600, the pressurecontrol valve can be opened and closed based on the measured pressure.The valve may stay open for a first duration (e.g., 30 milliseconds), atwhich point the pressure measured by the pressure transducer may reachthe maximum pressure set-point. The control system 310 may normally senda signal to close the valve. However, if there is a fault in thepressure regulation system 200 and the control system 310 fails to closethe pressure control valve, the control system 310 may continuemonitoring the elapsed time since the valve was opened. If the elapsedtime exceeds a predetermined time (e.g., two seconds), the controlsystem 310 may close the pressure control valve and/or send a faultsignal. Such embodiments may provide added safety in the event that thecontrol system 310 fails to regulate the pressure.

Algorithm 2—On-Off Control with Changing Set Points

FIG. 8 illustrates a control algorithm 700 of regulating pressure of theheat transfer medium during a thaw/cautery cycle according to anothernon-limiting exemplary embodiment. The control algorithm 700 can besubstantially similar to control algorithm 600. In one example, thecontrol algorithm 700 may be implemented when the pressure (as measuredby the pressure transducer) may not always respond instantaneously tothe opening and closing of valves. Accordingly, in some such examples,the pressure (as measured by the pressure transducer) may continuerising even after the valve is closed when the pressure set-point isreached. The control algorithm 700 may address such effects to provideconsistent and stable pressure.

At step 702, the pressure transducer measures pressure and sends themeasured pressure (or an electrical signal representative thereof) tothe control system 310. The control system 310, at step 704, receivesthe measured pressure (or an electrical signal representative thereof)and compares it to a minimum pressure set-point. If the measuredpressure is at or less than the minimum pressure set-point, at step 706,the control system 310 sends a signal to the valve controller to openthe pressure control valve. The control system 310 may continuemonitoring the pressure (via pressure received from the pressuretransducer) when the valve is open to determine, at step 708, if thepressure reaches and/or exceeds a maximum pressure set-point. If thecontrol system 310 determines that the measured pressure reaches and/orexceeds the maximum pressure set-point, at step 710, the control system310 sends a signal (or instructions) to the valve controller to closethe pressure control valve. At this point, the pressure (as measured bythe pressure transducer) may continue rising, before beginning todecrease. At optional step 712, the control system 310 may compare thevalue of pressure before the pressure began decreasing to a firstpressure. If the pressure (as measured by the pressure transducer)reached and/or exceeded the first pressure (after the pressure controlvalves were closed), at optional step 714, the control system 310 maydecide that the minimum pressure set-point may have to be offset, oradjusted, so as to result in a lower deviation from a desired nominalpressure (as will be described with respect to FIG. 9).

At step 714, the control system 310 may calculate an offset and adjustthe minimum pressure set-point by an amount corresponding to the offset.In an example, the offset may be a difference between the first pressureand the maximum pressure set-point. In this example, the minimumpressure set-point may be adjusted (lowered) by the offset amount.Accordingly, for the subsequent cycle, the pressure control valve maynot open until the newly-lowered, or adjusted, minimum pressureset-point is reached. In turn, the offset from the maximum set-point mayalso be adjusted for subsequent cycles so that the range of pressurebetween adjusted set-points is less compared to initial set-pointvalues.

In some advantageous embodiments, the first pressure can be greater thanthe maximum pressure set-point, and the second pressure can be less thanthe minimum pressure set-point. In additional and alternativeembodiments, the first pressure and the second pressure may not beconstant throughout the thaw (or cautery) cycle, and may be adjustedeach time the pressure control valve is opened and closed. In furtheradditional and alternative embodiments, the first pressure and thesecond pressure may eventually, over time, equal the maximum pressureset-point and the minimum pressure set-point respectively. In suchadvantageous embodiments, the pressure (as measured by the pressuretransducer) may eventually decrease monotonically (rather than increaseinitially and then decrease) after the pressure control valve is closed.In this way, the adjustment made to one or both of the set-points isreduced over pressure cycles, one cycle compared to a subsequent cycle,so that the adjustment tends to zero and the effective pressure alignswith the target nominal pressure.

In an example implementation of control algorithm 700, the pressurecontrol valve can be opened and closed based on the measured pressureand the pressure set-points. If the pressure is below the minimumpressure set-point, the control system 310 may send a signal to open thepressure control valve. The pressure may continue increasing, andeventually reach the maximum pressure set-point. The control system 310may send a signal to close the pressure control valve. Due to effectssuch as delay in valve opening and closing in response to the signalsfrom the control system 310, blockages, etc., the pressure measured bythe pressure transducer may continue increasing, for example, until thefirst pressure before beginning to decrease again. The first pressurecan be greater than the maximum pressure set-point. Accordingly, thecontrol system 310 may not open the pressure control valve when theminimum pressure set-point is reached if the pressure reached and/orexceeded the first pressure. The control system 310 may wait until thepressure reaches a second pressure before the pressure control valve isopened again. When the pressure reaches the second pressure, thepressure control valve is opened.

The minimum pressure set-point may be, for instance, about 450 psi(about 30 bar) in one example involving argon as the heat transfermedium. In this example, the maximum pressure set-point may be, forinstance, about 500 psi (about 35 bar). The first pressure can be, forinstance, about 550 psi (about 38 bar). Accordingly, the control system310 may not open the pressure control valve when the minimum pressureset-point of about 450 psi is reached if the pressure reached and/orexceeded the first pressure of about 550 psi. In this example, thepressure continues to decrease until a second pressure of about 400 psi(about 28 bar) is reached. When the pressure reaches the secondpressure, the pressure control valve is opened.

The control system 310 may dynamically adjust the values of firstpressure and second pressure that correspond to valve opening andclosing based on the measured pressure at subsequent cycles of valveopening and closing based on offsets between the measured pressure andthe minimum and maximum pressure set-points just prior to or shortlyfollowing valve opening and valve closing respectively. Further, as willbe described further below, the control system can also determine theminimum and maximum pressure set-points based on the type of thecryoprobe in operative communication therewith.

In another example, the pressure may not reach as high as the firstpressure during a subsequent cycle after one cycle of pressureregulation according to control algorithm 700. After the pressurecontrol valve is closed, the pressure may, for instance, reach a lowervalue of a third pressure. Accordingly, in the next subsequent cycle,the control system 310 may wait until the pressure reaches, for example,a fourth pressure before the pressure control valve is opened. In someoptional advantageous embodiments, the pressures at the time of openingand closing may eventually converge to the minimum pressure set-pointand maximum pressure set-point respectively. The control system 310 maydynamically adjust the values of first pressure, second pressure, thirdpressure and fourth pressure (as well as subsequent pressures) thatcorrespond to valve opening and closing based on the measured pressureat various points in the cycle, and the offsets between the measuredpressure and the minimum and maximum pressure set-points. Further, aswill be described further below, the control system can also determinethe minimum and maximum pressure set-points based on the type of thecryoprobe in operative communication therewith.

In some such examples involving argon as the heat transfer medium, ifthe maximum pressure set-point is about 500 psi, the first pressure isabout 550 psi, the minimum pressure set-point is about 450 psi and thesecond pressure of about 400 psi, the third pressure can be about 525psi (about 36 bar) and the fourth pressure can be about 475 psi (about33 bar).

The control system 310 may normally send a signal to close the valve.However, if there is a fault in the pressure regulation system 200 andthe control system 310 fails to close the pressure control valve, thecontrol system 310 may continue monitoring the elapsed time since thevalve was opened. If the elapsed time exceeds a predetermined time(e.g., two seconds), the control system 310 may close the pressurecontrol valve and/or send a fault signal. Such embodiments may provideadded safety in the event that the control system 310 fails to regulatethe pressure.

FIG. 9 illustrates an example of pressure transducer data in response toopening and closing the pressure control valve. At time t₀, the pressuretransducer begins collecting pressure data (e.g., as illustrated bysteps 602 and 702 of control algorithms 600 and 700 respectively). Attime t₁, the pressure measured by the pressure transducer (indicated bysolid line in FIG. 9) is less than the minimum pressure set-point (e.g.,as illustrated by steps 604 and 704 of control algorithms 600 and 700respectively), and the control system 310 sends a signal (orinstructions) to open the pressure control valve (e.g., as illustratedby steps 606 and 706 of control algorithms 600 and 700 respectively).The pressure measured by the pressure transducer begins increasing. Attime t₂, the pressure measured by the pressure transducer reaches themaximum pressure set-point (e.g., as illustrated by steps 608 and 708 ofcontrol algorithms 600 and 700 respectively). At this point, the controlsystem 310 sends a signal (or instructions, as illustrated, for example,by steps 610 and 710 of control algorithms 600 and 700 respectively) toclose the pressure control valves.

In some optional embodiments, the pressure measured by the pressuretransducer may begin decreasing monotonically following the closure ofthe pressure control valve until the pressure control valve is openedagain. Alternatively, in other optional embodiments, the pressuremeasured by the pressure transducer may continue increasing (asindicated by the dashed line in FIG. 9) even after the pressure controlvalve has been closed until time t₃ before decreasing.

In some such optional embodiments, the pressure measured by the pressuretransducer may reach and/or exceed a first pressure at time t₃. In suchoptional embodiments, as described above, the control system 310 mayallow the pressure to continue decreasing further lower than the minimumpressure set-point to reduce the chances of pressure overshooting themaximum pressure set-point during the next instance of the pressurecontrol valve being opened. Accordingly, the pressure (as measured bythe pressure transducer) is allowed to decrease to a second pressure(less than the minimum pressure set-point) at time t₄, at which pointthe pressure control valve is opened again.

FIG. 9 also illustrates the desired nominal pressure as a solid line.The desired nominal pressure can be a cycle-average pressure and may bethe pressure of the heat transfer medium downstream of the pressurecontrol valve (e.g., when in the supply tube of the cryoprobe ordownstream thereof). The desired nominal pressure may remain generallyconstant over time.

Also illustrated in dashed lines in FIG. 9 is an effective averagepressure. The effective average pressure may be a cycle-averaged valuerepresenting a cycle-average over a single cycle. As describedpreviously, due to effects such as delay in valve opening and closing,physical blockages, etc., pressure measured by the transducer may notinstantaneously respond to the opening and closing of valves and maycontinue rising even after the valve is closed. Accordingly, theeffective average pressure may oscillate about the desired normalpressure. Over time, as a result of the control system adjusting thevalve opening and closing to ensure that measured pressures correspondto minimum and maximum pressure set-points respectively (e.g., as setforth in algorithm 700 illustrated in FIG. 8), the effective averagepressure may converge (over several cycles of valve opening and valveclosing) to reach the desired nominal pressure as shown in FIG. 9.

Algorithm 3—Pressure Set-Point Levels Based on Needle Type

FIG. 10 illustrates a method 900 of controlling the flow of the heattransfer medium during a thaw cycle according to a non-limitingexemplary embodiment. The method 900 can advantageously permit differenttypes of cryoprobes (e.g., with different probe shaft outer diameters,and/or different freezing/thawing properties) to be controlledindependently. In such cases, the pressure set-points described abovecan differ. Accordingly, method 900 can determine the pressureset-points at which the heat transfer medium may have to be supplied toprovide effective heat distribution during thawing (or cautery), withouthaving freezing and/or iceball formation for a particular probe type.

At step 902 a control system such as control system 310 can (e.g., viathe processor) read information regarding the cryoprobe(s) connected toeach flow channel (216 a, 216 b, 216 c, 216 d, . . . 216 n). Theinformation may be stored in electronic circuitry (e.g., a chip) on thecryoprobe. The control system 310 can, at step 904, determine pressureset-points for each of the channels based on the information regardingthe cryoprobe(s). In one example, optionally, the pressure set-pointsfor different types of cryoprobes may be previously determined (e.g.,experimentally) and stored in a memory or storage in operativecommunication (e.g., wired or wireless) with the control system 310.Alternatively, in another example, as another option, the pressureset-points may be determined empirically.

At step 906, the control system 310 can actuate the pressure controlvalves (S₁, S₂, S₃, S₄, . . . S_(n)) according to a control algorithm(described above, for instance, control algorithm 600 or controlalgorithm 700 or variants thereof) and use the pressure set-pointsdetermined at step 904. For instance, the values of maximum and minimumpressure set-points may be determined by the control system 310 at step904, and used in conjunction with control algorithms 600 or 700.Optionally, as described above with respect to FIG. 8, the algorithm ofFIG. 10 can also dynamically adjust the pressure set-points duringoperation, such that the measure pressure, over time, generallycorresponds to a desired effective pressure.

In optional embodiments, when the method 900 is used in conjunction withcontrol algorithm 700, the control system 310 can determine and set oneor more of the maximum pressure set-point, minimum pressure set-point,first pressure and second pressure for each flow channel (one or more of216 a, 216 b, 216 c, 216 d) based on the type of the cryoprobe connectedto a corresponding flow channel and/or its freeze/thaw properties.

An example implementation of the method 900 is as follows. A firstcryoprobe 100 a and a second cryoprobe 100 b may be connected to a firstflow channel 216 a and a second flow channel 216 b. The control system310 may determine (e.g., based on previous data, experiment, empiricalmethods) that a pressure set-point for the first cryoprobe 100 a isabout 500 psi and the pressure set-point for the second cryoprobe 100 bis about 450 psi. In such cases, the control system 310 can actuate afirst pressure control valve S₁ fluidly coupled to the first flowchannel 216 a according to the control algorithm (600, 700 or 1000) suchthat the pressure in the first flow channel 216 a is about 500 psi. Thecontrol system 310 can also actuate the second pressure control valveS₂(independently of the first pressure control valve) such that thepressure in the second flow channel 216 b is about 450 psi. Additionalor alternative implementations of method 900 are also contemplated.

Algorithm 3—Duty Cycling (Older Description)

FIG. 10 illustrates a control algorithm 1000 of adjusting pressure ofthe heat transfer medium according to a non-limiting exemplaryembodiment. The method can be performed with a cryosurgical systemaccording to any of the disclosed embodiments. The method can be in theform of machine-readable (or computer executable) instructions andprovided to (e.g., programmed in the memory of) the control system 310.At step 1002, the control system 310 can determine (e.g., based on userinput received at step 1001) whether the cryosurgical system isperforming a thaw (or cautery) operation or a freeze operation. Thecontrol system 310 can make such a determination, for instance, based onoperator input. If the control system 310 determines the system is aboutto perform a freeze cycle, optionally, the control system 310 candetermine (based on operator input, or stored program settings), whichof the cryoprobes would be performing the freeze operation. At step1006, the control system 310 can electrically communicate with thepressure control valves (S₁, S₂, S₃, S₄, . . . S_(n)) and send anelectrical signal that switches the pressure control valves (S₁, S₂, S₃,S₄, . . . S_(n)) from their closed state to the open state.Advantageously, at this step, the control system 310 can determine whichof the pressure control valves (S₁, S₂, S₃, S₄, correspond to cryoprobesperforming freeze operation, and selectively actuate those pressurecontrol valves (S₁, S₂, S₃, S₄, . . . S_(n)). Alternatively, the controlsystem 310 can actuate all the pressure control valves (S₁, S₂, S₃, S₄,. . . S_(n)). In further advantageous aspects, the control system 310can control freeze performance by monitoring pressure measurement datafrom the pressure transducers (PT₁, PT₂, PT₃, PT₄, . . . PT_(n)) andadjust freeze performance. For instance, the control system 310 canclose (and/or repeatedly open and close) the pressure control valves(S₁, S₂, S₃, S₄, . . . S_(n)) once a desired freeze performance (e.g.,as indicated by an iceball size) is reached.

If the control system 310 determines that the cryosurgical system isperforming the thaw operation (or cautery), the control system 310receives pressure measurement data from the pressure transducers (PT₁,PT₂, PT₃, PT₄, . . . PT_(n)) connected to the pressure control valves atstep 1008. At step 1010, the control system 310 determines whether thepressure measured downstream (e.g., as the fluid travels toward thecryoprobe) of the pressure control valve is within a predeterminedpressure range. As described previously, the predetermined range can beless than the second pressure (e.g., less than which the heat transfermedium is in a non-cryogenic state). If the control system 310determines that the pressure is not within the predetermined pressurerange, at step 1012, the control system 310 actuates (e.g., by sendingan electrical signal) the pressure control valves repeatedly so as toswitch between open state and closed state of the pressure controlvalves. The control system 310 can perform this step until the pressuredownstream (e.g., as the fluid travels toward the cryoprobe) of thepressure control valve is within the predetermined pressure range.

In advantageous aspects of the control algorithm 1000, the controlsystem 310 can actuate the pressure control valve over several repeatedcycles during the thaw process (or cautery), wherein for each cycle, thepressure control valve is in the open state for a first time intervaland in the closed state for a second time interval. The first and secondtime intervals can be chosen to result in desired pressure downstream ofthe pressure control valve(s). In certain additional embodiments, thepressure control valve(s) can be in the open state for a durationcorresponding to the freeze operation. In some embodiments, the ratio ofa time over which the pressure control valve of the one or more pressurecontrol valves remains open relative to a time over which the pressurecontrol valve of the one or more pressure control valves remains closedcan be between about 5% and about 80%.

Embodiments according to the present disclosure provide severaladvantages. Embodiments provide the ability to use a single heattransfer medium for both freeze and thaw (or cautery) operations,thereby eliminating additional fluid sources. Further, by using the heattransfer medium to distribute heat during the thaw cycle (or cautery),heat generated by the heaters within cryoprobe can be more evenlydistributed such that temperatures measured at various points along alength of the cryoprobe may not vary drastically. Certain embodimentspermit adjusting the pressure of the heat transfer medium over a widerange without the use of additional pressure regulators or solenoids.Several of the disclosed embodiments provide a compact and efficientlypackaged cryoablation system.

Non-limiting embodiments have been described. These and furtherembodiments are within the scope of the following claims.

The invention claimed is:
 1. A pressure regulation system for a surgicalsystem for regulating a pressure of a heat transfer medium supplied to asurgical tool from a heat transfer medium source, the surgical toolbeing connectable to the surgical system, the pressure regulation systemcomprising: a pressure control valve, the pressure control valvecomprising an inlet being fluidly connectable to the heat transfermedium source, and an outlet being fluidly connectable to the surgicaltool, the pressure control valve being actuable so as to be in an openstate so as to permit passage of the heat transfer medium therethrough;and a closed state so as to reduce the passage of the heat transfermedium therethrough, wherein a quantity of heat transfer medium flowingthrough the pressure control valve in the closed state is less than aquantity of heat transfer medium flowing through the pressure controlvalve in the open state; and a control system operatively coupled to thepressure control valve, the control system being configured to: receivea signal corresponding to a pressure of the heat transfer medium at ordownstream of the outlet of the pressure control valve, determinewhether the pressure is at or less than a minimum pressure set-point, ifthe control system determines that the pressure is at or less than theminimum pressure set-point, send a first signal to actuate the pressurecontrol valve to the open state, determine whether the pressure is abovea maximum pressure set-point, and if the control system determines thatthe pressure is above the maximum pressure set-point, send a secondsignal to actuate the pressure control valve to the closed state;wherein the control system is configured to determine if the pressureincreases to a first pressure exceeding the maximum set-point pressureafter the pressure control valve is actuated to a closed state, and toadjust the minimum pressure set-point by an offset equal to a differencebetween the first pressure and the maximum pressure set-point.
 2. Acryosurgical system, comprising: one or more cryoprobes; one or morepressure control valves, each pressure control valve being fluidlycoupled with at least one cryoprobe, each pressure control valve beingindependently actuable with respect to other pressure control valves soas to be in an open state so as to permit passage of the heat transfermedium therethrough; and a closed state so as to reduce the passage ofthe heat transfer medium therethrough, wherein a quantity of heattransfer medium flowing through the pressure control valve in the closedstate is less than a quantity of heat transfer medium flowing throughthe pressure control valve in the open state; one or more pressuretransducers, each pressure transducer being fluidly coupled to acorresponding pressure control valve; and a control system in operativecommunication with each pressure control valve, the control system beingconfigured to: determine whether at least one cryoprobe is performing afreeze operation or a thaw operation; if the control system determinesthat the at least one cryoprobe is performing the freeze operation, openthe pressure control valve fluidly coupled to the at least onecryoprobe, such that a heat transfer medium is supplied through thepressure control valve to the at least one cryoprobe, so as to result incryogenic expansion and/or freezing, and if the control systemdetermines that the at least one cryoprobe is performing the thawoperation, actuate the pressure control valve to repeatedly open andclose the pressure control valve fluidly coupled to the at least onecryoprobe based on pressure measured by the pressure transducer, suchthat the pressure of the heat transfer medium supplied through thepressure control valve is less than a pressure corresponding tocryogenic expansion and/or freezing produced from the heat transfermedium, wherein the control system is configured to actuate eachpressure control valve independently of other pressure control valvesbased on pressure measured by each of the pressure transducer fluidlycoupled to the corresponding pressure control valve, and wherein thecontrol system is configured to determine if the pressure increases to afirst pressure exceeding the maximum set-point pressure after thepressure control valve is actuated to a closed state, and to adjust theminimum pressure set-point by an offset equal to a difference betweenthe first pressure and the maximum pressure set-point.
 3. The pressureregulation system of claim 1, wherein the control system is configuredto send a third signal to actuate the pressure control valve to an openstate if the control system determines, after the pressure control valveis actuated to a closed state, that the pressure is at or less than theadjusted value of the minimum pressure set-point.
 4. The pressureregulation system of claim 1, wherein the control system is configuredto measure an elapsed time after the pressure control valve is actuatedto an open state, and compare the elapsed time to a predetermined time.5. The pressure regulation system of claim 4, wherein the control systemis configured to send the second signal to actuate the pressure controlvalve to a closed state if the elapsed time exceeds the predeterminedtime.
 6. The pressure regulation system of claim 4, wherein the controlsystem is configured to send a fourth signal indicative of a faultcondition, if the elapsed time exceeds the predetermined time.
 7. Thepressure regulation system of claim 1, wherein the pressure controlvalve is co-operable with a valve actuator and the valve actuator isresponsive to a control signal from the control system for actuated thevalve to an open state and to a closed state.
 8. The pressure regulationsystem of claim 7, wherein the actuator comprises a solenoid.
 9. Thepressure regulation system of claim 1, further comprising a pressuretransducer configured to measure the pressure of the heat transfermedium at the outlet or downstream of the outlet of the pressure controlvalve.
 10. A cryosurgical system, comprising: one or more cryoprobes forinsertion in a patient for performing a cryosurgical procedure, eachcryoprobe being configured to receive a heat transfer medium conveyedfrom a source of heat transfer medium; a pressure regulation system forregulating the pressure of a heat transfer medium conveyed to the oreach cryoprobe, comprising: one or more pressure control valves, eachpressure control valve being operable to place the source of heattransfer medium in fluid communication with at least one cryoprobe, eachpressure control valve being actuable so as to be in an open state so asto permit passage of the heat transfer medium therethrough, or in aclosed state so as to reduce passage of the heat transfer mediumtherethrough, wherein a quantity of heat transfer medium flowing throughthe pressure control valve in the closed state is less than a quantityof heat transfer medium flowing through the pressure control valve inthe open state, and one or more pressure transducers, each pressuretransducer being configured to measure a pressure of the heat transfermedium at or downstream of an associated pressure control valve; and acontrol system operably connected to said one or more pressure controlvalves and said one or more pressure transducers, and configured to:determine if the pressure received from a said pressure transducer is ator less than a minimum pressure set-point, send a first signal toactuate an associated pressure control valve to an open state if thepressure is at or less than the minimum pressure set-point, determine ifthe pressure received from a said pressure transducer is at or greaterthan a maximum pressure set-point, and send a second signal to actuatean associated pressure control valve to a closed state if the pressureis greater than the maximum pressure set-point; wherein the controlsystem is configured to determine if the pressure increases to a firstpressure exceeding the maximum set-point pressure after the pressurecontrol valve is actuated to a closed state, and to adjust the minimumpressure set-point by an offset equal to a difference between the firstpressure and the maximum pressure set-point.
 11. The cryosurgical systemof claim 10, comprising a plurality of said cryoprobes and wherein eachcryoprobe is independently operable relative to other cryoprobes, suchthat the control system is arranged to determine the maximum pressureset-point and the minimum pressure set-point corresponding to eachcryoprobe, and to actuate to an open state and a closed state thepressure control valves connected to respective cryoprobes based on thecorresponding maximum pressure set-point and the minimum pressureset-point.
 12. The cryosurgical system of claim 10, wherein eachpressure control valve comprises a valve actuator for actuating thevalve to a closed state and an open state and the actuator is responsiveto a control signal from the control system for controlling actuation.13. The cryosurgical system of claim 10, wherein each cryoprobecomprises an electrical heater responsive to a control signal from thecontrol system for heating a heat transfer medium in the cryoprobeduring a thaw operation.
 14. The cryosurgical system of claim 13,wherein the control system is arranged to regulate the pressure of heattransfer medium conveyed to the or each cryoprobe in a thaw operation sothat the pressure is at or lower than the maximum pressure set-point atwhich the heat transfer medium is in a non-cryogenic state fordistributing heat generated by the electrical heater for transfer to apatient.
 15. The cryosurgical system of claim 10, wherein the controlsystem is arranged to regulate the pressure of heat transfer mediumconveyed to the or each cryoprobe so that the pressure is greater thanthe maximum pressure set-point at which the heat transfer medium is in acryogenic state to freeze and/or cryogenically ablate tissue surroundingthe cryoprobe during a freeze operation.
 16. The cryosurgical system ofclaim 15, wherein the control system is arranged to cause each pressurecontrol valve to be actuated to an open state for the duration of thefreeze operation.
 17. The cryosurgical system of claim 10, wherein theheat transfer medium is argon.
 18. The cryosurgical system of claim 17,arranged for fluid communication with a source of heat for supplyingheat transfer medium at a pressure of between about 1000 psi (about 70bar) and about 4000 psi (about 275 bar) upstream of the pressureregulation system.
 19. The cryosurgical system of claim 18, wherein theminimum pressure set-point is at least about 200 psi (about 15 bar). 20.The cryosurgical system of claim 18, wherein the maximum pressureset-point is at or below about 1000 psi (about 70 bar).
 21. Thecryosurgical system of claim 10, wherein, when the pressure receivedfrom the pressure transducer of the one or more pressure transducers isat or greater than a maximum pressure set-point, the control systemsends a signal to decrease the ratio of a time over which the pressurecontrol valve of the one or more pressure control valves remains openrelative to a time over which the pressure control valve of the one ormore pressure control valves remains closed.
 22. A method of adjustingpressure in a cryoprobe, comprising: providing a cryosurgical system,comprising one or more cryoprobes, one or more pressure control valves,each pressure control valve being fluidly coupled with at least onecryoprobe, one or more pressure transducers, each pressure transducerbeing fluidly coupled to a corresponding pressure control valve, and acontrol system in operative communication with each pressure controlvalve; determining whether at least one cryoprobe is performing a freezeoperation or a thaw operation; if the at least one cryoprobe isperforming the freeze operation, opening the pressure control valvefluidly coupled to the at least one cryoprobe, such that a heat transfermedium is supplied through the pressure control valve to the at leastone cryoprobe, so as to result in cryogenic expansion and/or freezing,and if the at least one cryoprobe is performing the thaw operation,actuating the pressure control valve to repeatedly open and close thepressure control valve fluidly coupled to the at least one cryoprobebased on pressure measured by the pressure transducer, such that thepressure of the heat transfer medium supplied through the pressurecontrol valve is less than a pressure corresponding to cryogenicexpansion and/or freezing produced from the heat transfer medium,wherein the control system actuates each pressure control valveindependently of other pressure control valves based on pressuremeasured by each of the pressure transducer fluidly coupled to thecorresponding pressure control valve, and wherein the control system isconfigured to determine if the pressure increases to a first pressureexceeding the maximum set-point pressure after the pressure controlvalve is actuated to a closed state, and to adjust the minimum pressureset-point by an offset equal to a difference between the first pressureand the maximum pressure set-point.